(a) Field of the Invention
The present invention relates to a novel process for preparing packings for liquid chromatography.
Liquid chromatography is widely used as an important means of analysis and separation in fields of pharmaceuticals, foods, natural compounds and the like. Widely-used packings for liquid chromatography are porous silica gel which is surface-modified with alkyl or the like. The most general silica gel surface-modified is that octadecyl (ODS) is introduced onto OH groups on the surface through siloxane bond, and silica gel bonded with octyl, butyl, methyl groups and the like are also known. The alkyl sometimes has functional group(s) such as phenyl, amino and cyano at its terminal.
However, even if the surface of the silica gel is modified by alkylation, some silanol groups (Si—OH) still remain on the silica surface. The residual silanol group causes the problems that when a basic compound is an object of analysis or preparative separation, the compound is not eluted because of strong interaction between the silanol group and the compound, and tailing of peaks is observed. For the purpose of preventing these phenomena, it is necessary to endcap the residual silanol groups by secondary silylation after surface modification to make the silica surface more inactive.
(b) Description of the Prior Art
Conventional endcapping methods are as follows. Japanese Laid-open Patent Publication No. 212058/1992 describes a method of reacting specified cyclosiloxane, hydrodienesiloxane, alkoxysilane or siloxane as an endcapping agent in a gas phase with silica gel or porous glass which is surface-modified with chemical modifying agents to link the endcapping agent to residual silanol groups on the silica gel surface. Japanese Laid-open Patent Publication No. 304371/1996 describes a method of reacting specified polydimethylsiloxane, polyphenylmethylsiloxane, polydiphenyldimethylsiloxane, polycyanopropylmethyldimethylsiloxane, polycyanopropylmethylphenylmethylsiloxane and the like with silica gel. Japanese Laid-open Patent Publication No. 73579/1998 describes a method of reacting at least two of endcapping agents such as specified silazane, disilazane, siloxane and polysiloxane at 180° to 240° C. in a gas phase with silica gel which is surface-modified with chemical modifying agents.
In these conventional methods, however, the reactions require high temperatures, and the residual silanol groups on the silica surface cannot be sufficiently reduced. Accordingly, packings obtained by these methods cannot prevent tailing of the basic compounds.
In view of the above-mentioned background, an aim of the present invention is to provide packings for high performance liquid chromatography whose residual silanol groups are remarkably reduced and which remarkably prevent the tailing of the basic compounds.